Unrestrained Roof Construction
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Standing seam decking or decking which is deemed to afford little or no restraint to the Purlin top flange requires special consideration.
To determine the optimum Purlin section our computer software should be used which takes into account the buckling resistance for the unrestrained Purlin section.
Alternatively the published load tables may be utilised, providing SRS Type Struts are included, so that the maximum unrestrained distance between Struts does not exceed 2000mm - Ultimate Wind Uplift Values are as for Ultimate Down Load in this situation.
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Note:- Where screw fixed rigid liner tray of a thickness greater than 0.3mm (Steel) or 0.5mm (Aluminium) is utilised the Purlin may be designed as fully restrained. If the restraint afforded to the purlins is in doubt consult cladding supplier for confirmation.